Introduction: Children and adolescents with syncope are frequent patients in a general practitioner’s or paediatrician’s office. Syncope is a sudden, reversible, short and spontaneously resolving loss of consciousness associated with transient global cerebral hypoperfusion. The pattern of metabolic and clinical disorders resulting from brain ischaemia has been well described in patients with cerebral stroke. Due to brain ischaemia during stroke, the blood–brain barrier is broken down, which results in the appearance of S100B protein in the cerebrospinal fluid. Its concentration increases with increasing extent of ischaemia. The aim of the study was to assess whether adolescents with syncope present elevated serum S100B protein concentrations. Material and methods: The analysis involved 70 adolescents at 14–18 years of age (average age: 15.5), including 32 syncope patients and 38 controls. The basic diagnostic test was a tilt test performed in accordance with the Westminster protocol. S100B assay was conducted by collecting blood samples directly before a tilt test as well as 6 and 24 hours afterwards. Results: There were no differences between patients and controls in S100B levels at baseline and after 6 and 24 hours. Conclusions: The results of the study do not confirm the hypothesis that during syncope in adolescents, the brain tissue becomes damaged, which would be indicated by elevated serum S100B protein level. This research project requires continuation, and further analyses should be conducted taking into account various types of syncope, particularly the cardioinhibitory one, during which cardiac asystole of 3–15 seconds (or even longer) is observed.